1. Field of the Invention
The present invention relates generally to disk drives, and in particular to a disk drive including head stack assembly including a constrained layer damper disposed upon an actuator body lateral surface.
2. Description of the Prior Art
The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA). The spindle motor includes a spindle motor hub that is rotatably attached to the disk drive base. The hub has an outer hub flange that supports a lowermost one of the disks. Additional disks may be stacked and separated with annular disk spacers that are disposed about the hub. The head stack assembly has an actuator assembly having at least one transducer head, typically several, for reading and writing data from and to the disk. The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
The head stack assembly includes an actuator assembly, at least one head gimbal assembly, and a flex circuit cable assembly. A conventional “rotary” or “swing-type” actuator assembly typically includes an actuator having an actuator body. The actuator body is configured to rotate on a pivot assembly between limited positions about an axis of rotation. A coil support extends from one side of the actuator body. A coil is supported by the coil support and is configured to interact with one or more permanent magnets to form a voice coil motor. One or more actuator arms extend from an opposite side of the actuator body. A head gimbal assembly includes a transducer head, typically a magneto-resistive (“MR”) head, which is distally attached to each of the actuator arms. To facilitate rotational movement of the actuator, the actuator assembly further includes the actuator body that has a bore and a pivot bearing cartridge engaged within the bore. Each magnetic disk includes opposing disk surfaces. Data may be recorded on a single surface or both along data annular regions. As such, the head stack assembly may be pivoted such that each transducer head is disposed adjacent the various data annular regions from adjacent the outer diameter to the inner diameter of each disk.
The actuator assembly has various natural modes of vibration. One such mode is referred to as a “butterfly” mode or the first principal bending mode. During such a butterfly mode of vibration, the actuator arms and the coil support slightly flex or bend toward and away from each other in a plane orthogonal to the axis of rotation and the heads move away from its position on the disk. The butterfly mode of vibration can be excited by those electromagnetic forces in a direction perpendicular to a longitudinal axis of the actuator produced by the current through the coil and the electromagnetic forces interaction with the magnetic field of the magnets. Thus, if the natural frequency of the butterfly mode of vibration is 5 kilo hertz and the applied current into the coil has a 5 kilo hertz component, then this will result in the potential for undesirable excitation of the butterfly mode of vibration. While a filter, such as a notch filter, may be used to remove the frequency component corresponding to the natural frequency of the butterfly mode of vibration, which may negatively impact the capability of the actuator servo control system by reducing its bandwidth. Accordingly, there is a need in the art for a disk drive having an improved actuator assembly design in comparison to the prior art.